Nitrate leaching from a free-draining volcanic soil irrigated with municipal sewage effluent in New Zealand

Land application of municipal sewage effluent is becoming increasingly popular worldwide as a means of disposal, treatment, nutrient recycling, irrigation to meet plants' water requirements, and groundwater recharge. Nitrate leaching from a volcanic soil (Typic Udivitrand) was investigated under a Pinus radiata plantation near Rotorua, New Zealand, which had received, on average, 0, 29, and 88 mm per week of tertiary-treated municipal sewage effluent for the previous 4 years. Four replicates of undisturbed soil monolith lysimeters (200 mm diameter×200 mm depth) from surface soil from each treatment were used to study the influence of the three different rates of effluent application on N leaching. A rapid emergence of nitrate–N occurred in the drainage samples, and indicated that approximately up to half of soil nitrate was readily leached beyond the topsoil. Nitrate–N concentrations in the drainage water increased substantially with effluent application rate, almost reaching the World Health Organisation recommended limits (approximately 10 g m −3) in plots receiving effluent at the highest rate. Given that nitrate leaching from the soils may threaten the viability of the land treatment system, due to large N loads being observed in streams which drain irrigated catchments during winter periods, possible strategies for minimising nitrate leaching losses under effluent irrigation may need to be considered.